For offset, I would like to steal from Dudesky (as I had the same question a month or two back)
Originally Posted by Dudesky
(Stolen from Yokohama's website):
Also, the 318 generally has an offset of 47mm.
As for worthwhile mods, imho, Bilstein Sports are a great investmest. I also own a 318is, and as our cars are not very fast, a little help in the corners goes a long way.
I actually got the biggest compilment on my car a few weeks ago when I was on a BMW drive being followed by a 1998 328is.
"What did you do to your car??? I could barely keep up with it!"